This invention relates generally to mechanical suspension devices for limited linear or reciprocating motion applications. Specifically this invention relates to a mechanical flexure suspension for use with a reciprocating alternator power conversion system for Free-Piston Stirling Engines (FPSE). The current invention however is easily adaptable for use with virtually any linear limited motion or reciprocating device, ie. linear force motors, vibration detectors, etc..
Free Piston Stirling Engines (FPSE) have just two moving parts: a displacer and a piston; both in linear, reciprocating motion during operation. Power conversion systems, including reciprocating alternators, for use with FPSEs have been recognized as having the potential for simple, efficient, reliable, virtually maintenance free operation for use in applications such as in outerspace. The major problems confronting designers of these systems are the limitations of current bearing designs and the failure thereof. These nominally non-contacting sliding bearing types (hydrostatic or hydrodynamic gas, magnetic) nonetheless exhibit some contact of the displacer and piston/alternator plunger at start up and shut down, which ultimately leads to wear of the bearings and failure of the system. Additionally, each of the aforementioned bearing systems require additional support systems or devices which rob the power conversion system of output power, increase system cost and complexity, and dramatically reduce reliability.
It was recognized by the inventors hereof that a flexible mechanical suspension system used in combination with a reciprocating alternator would alleviate many of the problems associated with the previously mentioned bearing systems.
Various types of mechanically-flexing suspension devices are known in the art. Each of these systems has various shortcomings which render them unacceptable for use with a reciprocating alternator, especially that proposed by the inventors, which itself is the subject of a copending application, which alternator requires a suspension with a relatively long stroke capability, high torsional and radial stiffness, and, to satisfy a requirement for use in space power systems, an extremely long life span.
Of the known art in flexible mechanical devices, helically wound wire devices (commonly called coil springs) have neither the radial nor torsional stiffness required for the subject application. Bellows devices have substantially no radial stiffness. Diaphram type devices such as those described in U.S. Pat. Nos. 4,792,708 to Boyer; 4,638,830 to Brown et. ano.; 4,458,344 to Coogle; and 4,238,845 to Haggard et al. (more closely related in form to the present invention) have radial and torsional stiffness but lack sufficient axial flexibility to permit practical stroke length.
As will be evident from the detailed description, the subject strap-and-ring suspension provides all of the required attributes addressed above. In addition the design is well adapted for easy manufacture from rolled material stock.